MicroLogix 1200
MicroLogix Family Overview
Falling between Allen-Bradley’s larger CompactLogix / ControlLogix PLCs and their ‘tiny’ Micro PLCs, the MicroLogix PLC family is made up of five models each with unique features and target applications. Overall, the MicroLogix family is particularly well-positioned to handle single-machine control functionality that can also benefit from advanced communication, IO, recipe batching, PID control, small form factor, and human interface options.
The Allen-Bradley MicroLogix family of PLCs is based on two paramount design points: compact size and cost-effective modern process control. Below is a brief breakdown of the five series in the family.
- Bulletin 1761: MicroLogix 1000
- Ultra-compact, low cost, fixed I/O points
- Bulletin 1763: MicroLogix 1100
- Adds onboard LCD screens, embedded analog, and Ethernet
- Bulletin 1762: MicroLogix 1200
- Small size, scalable, expandable, uprgadable operating system
- Bulletin 1766: MicroLogix 1400
- Adds high speed counter, pulse train, and more expandability
- Bulletin 1764: MicroLogix 1500
- Modular, highly expandable design, high performance
In general, the MicroLogix family is centered around offering a single-device solution to small machine applications, containing a mix of embedded IO points and communication ports on the PLC itself. Often, all you’ll need for small applications is the PLC base unit alone. When additional IO or communication options are needed, the MicroLogix family shares expansion modules between series, allowing for expanding your PLC platform for larger projects.
Some components are shared across the MicroLogix series. Therefore, extra attention is needed when searching for compatible components. For example, the MicroLogix 1100, 1200, and 1400 series share add-on expansion IO modules, but controller and memory accessories are separate between models.
MicroLogix 1200 Overview
The MicroLogix 1200 series consists of five (5) models that vary in I/O, power supply voltages, and special connectivity capabilities. Originally introduced in the late 1990s as the mid-point between the 1000 and 1500 series, the 1200 series was designed to offer the higher-scale capabilities of the 1500 series in the ultra-compact footprint of the 1000 series. Rockwell Automation also introduced several first-time features in the 1200 series, such as removable write-on IO labels and finger-safe terminal blocks in their expansion modules. The series was also marketed as compatible with applications written for other series, allowing easy scalability between MicroLogix 1000 and 1500 applications, as well as SLC 500 series applications. While later advances in the 1100 and other models brought newer technology options to those series, the 1200 series continued to fill a need for high onboard IO counts, significant expandability, and competitive cost.
Across all MicroLogix 1200 controllers, we can find the following common features:
- Large 6 KB memory (4 KB User Program with 2 KB User Data) to solve a variety of applications.
- High-performance expansion I/O options (up to six modules depending on current/power budget).
- Four high-speed inputs (for controllers with 24V DC inputs) that can be used individually as latching (pulse-catch) inputs, event interrupts, or alternately combined as one 20 kHz high-speed counter featuring eight modes of operation.
- One high-speed output that can be configured as 20 kHz pulse train output (PTO) or as pulse width modulated (PWM) output (available on controllers with embedded 24V DC outputs).
- One 1-millisecond selectable timed interrupt (STI).
- High-resolution, 1-millisecond timers.
- The same advanced communication options as the MicroLogix 1000 controller, including peer-to-peer and SCADA/RTU networks, DF1 full-duplex, DF1 half-duplex slave, DH-485, and EtherNet/IP, plus DF1 half-duplex master, Modbus master and slave, and DF1 radio modem protocols.
- ASCII read/write capability.
- An additional Programming/HMI Port, providing connectivity to a DF1 full-duplex compatible device such as an operator interface or programming terminal (MicroLogix 1200R controllers only, catalog number 1762-LxxxxxR).
- Communication toggle pushbutton that allows the controller's Channel 0 port to toggle between user-configured communication parameters and factory default settings for an easy means to switch from Modbus RTU or ASCII protocols (which do not support programming) to DF1 full-duplex (to upload/download, monitor, or edit your program), so a programming computer can connect to a controller with an unknown or incorrect communication parameter settings for troubleshooting.
- Optional real-time clock, to allow control to be based on the actual time of day, day of the week, or other calendar-related timing.
- Optional memory module, for external program backup, transport, and transfer to another controller. Control program and data are securely backed up to internal flash memory when power is not applied.
- Data file download protection prevents critical user data from being altered via program downloads from programming computers or memory modules.
- Two built-in analog trim potentiometers.
- 32-bit signed integer math.
- Floating-point and double integer data file support.
- Built-in PID capabilities.
- Finger-safe terminal blocks meet global safety standards.
- Removable terminal blocks on 40-point controllers allow pre-wiring.
- Regulatory agency certifications for the worldwide market (CE, EAC, RCM, UL, c-UL, including Class 1 Division 2 Hazardous Location).
We find that the MicroLogix 1200 series fits best into applications where moderate I/O quantities and robust operator HMI interactions are called for. Available in either 24- or 40-point onboard I/O count versions, base models offer a fair amount of connectivity right out of the box, though limited to discrete signals only. Still, this discrete I/O base offers multiple advanced features, such as trim potentiometers, 20 kHz high-speed counters, interrupt inputs, and more, which allow for a wide variety of applications. To expand this I/O base, up to six (6) expansion modules can be added to the chassis, providing analog, sink/source discrete, RTD, resistance, thermocouple, AC Triac, DC solid-state, and other circuit options. Additional network connectivity options can also be found in AIC+, DeviceNet, and EtherNet interface modules. All in all, the MicroLogix 1200 fits quite well into moderately-sized machine applications that can benefit from advanced I/O and graphical operator interfaces.
Standard MicroLogix 1200 Models
The following bulleted list shows the six (6) catalog number models available in the MicroLogix 1200 PLC series. These models differ by supply power and I/O types. All chassis enclosures are physically the same between models, with only I/O assignments being different internally. Note that the I/O selections listed below are all embedded into each chassis, and additional capacity can be achieved using expansion modules regardless of the selected base unit.
- 1762-L24AWA(R): MicroLogix 1200, 120/240V AC Power, Onboard Standard I/O, no High-Speed I/O
- 1762-L40AWA(R): MicroLogix 1200, 120/240V AC Power, Additional Onboard Standard I/O, no High-Speed I/O
- 1762-L24BWA(R): MicroLogix 1200, 120/240V AC Power, Onboard Standard, Fast, and High-Speed I/O
- 1762-L40BWA(R): MicroLogix 1200, 120/240V AC Power, Additional Onboard Standard, Fast, and High-Speed I/O
- 1762-L24BXB(R): MicroLogix 1200, 24V DC Power, Onboard Standard, Fast, and High-Speed I/O
- 1762-L40BXB(R): MicroLogix 1200, 24V DC Power, Additional Onboard Standard, Fast, and High-Speed I/O
We’ll remind here again that the MicroLogix 1200 PLC has a Bulletin number of 1762, with compatible expansion modules under Bulletin 1762 (which may also indicate compatibility with 1100 and 1400 series), real-time clock modules under Bulletin 1762, memory modules under Bulletin 1762, communication interfaces under Bulletin 1761, and cables under Bulletin 1761.
Application Considerations
As with the other series in the MicroLogix family, our selection options for the 1200 series are fairly pre-defined for us. Functional, programmatic, and interface types are all standardized across the available catalog numbers, so our selection criteria for choosing a model to purchase is essentially around power and I/O types. Of the two, I/O selection should be the element warranting the most attention.
- 1762-L24AWA(R): This product has a line voltage rated at 120/240V AC. It has fourteen (14) 120V AC Inputs and ten (10) relay outputs.
- 1762-L40AWA(R): This product has a line voltage rated at 120/240V AC. It has twenty-four (24) 120V AC inputs and sixteen (16) relay outputs.
- 1762-L24BWA(R): This product has a line voltage rated at 120/240V AC. It has ten (10) standard 24V DC inputs, four (4) fast 24V DC inputs, ten (10) relay outputs, and four (4) 20 kHz high-speed inputs.
- 1762-L40BWA(R): This product has a line voltage rated at 120/240V AC. It has twenty (20) standard 24V DC inputs, four (4) fast 24V DC inputs, sixteen (16) relay outputs, and four (4) 20 kHz high-speed inputs.
- 1762-L24BXB(R): This product has a line voltage rated at 24V DC. It has ten (10) standard 24V DC inputs, four (4) fast 24V DC inputs, five (5) relay outputs, four (4) standard 24V DC FET outputs, one (1) fast 24V DC FET output, four (4) 20 kHz high-speed inputs, and one (1) 20 kHz high-speed output.
- 1762-L40BXB(R): This product has a line voltage rated at 24V DC. It has twenty (20) standard 24V DC inputs, four (4) fast 24V DC inputs, eight (8) relay outputs, seven (7) standard 24V DC FET outputs, one (1) fast 24V DC FET outputs, four (4) 20 kHz high-speed inputs, and one (1) 20 kHz high-speed output.
Have a standard relay control, stop-start type application? The base catalog model 1762-L24AWA (120V AC) or 1762-L24BXB (24V DC) will likely be sufficient. Adding instrument inputs for online process or condition monitoring, such as a pressure or temperature sensor? You’ll need to add an expansion module to work with the analog or sensor-specific resistance input. Adding even more complex process conditions, such as a high-speed counter input? Any of the models ended in …BWA or …BXB will have onboard high-speed I/O.
If your application calls for coordinated control functionality based on time-of-day criteria, add a Real-Time Clock module 1762-RTC, which also includes an onboard battery. If you’d like the added security of having onboard program backups, add a 1762-MM1 memory module. This memory module is purely for backups, auto-recovery, and transporting program copies away from the controller. It does not add additional system space to the onboard persistent memory capacity.
The MicroLogix 1200 series truly shines in advanced communication and operator interface schemes, using the special ‘R’ variant of each model. Every configurable model can include the last letter ‘R’ in its part number, which according to the part number matrix in the previous section, denotes adding a ‘Programming/HMI’ port to the system. This dedicated Programming / HMI port is provided in addition to the Channel 0 port onboard, offering an inexpensive means of providing an extra comm port that can be used for programming using a PC, as well as connecting an operator interface directly to the controller, saving the need for a separate switch. This additional port requires no configuration, picking up the same parameters as Channel 0 port. For even more unique customization, this port can be set to a ‘respond only’ mode, turning off full messaging for use in slave applications where only a response message direction is needed.